Abstract.
Comet Siding Spring approached Mars with a closest distance of ~140000 km in October 2014.
Such a close encounter of an active comet was said to be a once-in-one-million-year opportunity.
Due to enough outgas and dust release from the comet, a highly disturbed space environment around Mars has been expected, and detected.
Here we describe the plasma measurements conducted by ASPERA-3 instrument on board Mars Express.
ASPERA-3 was operated to detect changes of plasma environment throughout the comet encounter.
We will discuss the influence of highly disturbed space environment influences to the Martian upper atmosphere.